lttng-snapshot(1)

1LTTNG-SNAPSHOT(1)                LTTng Manual                LTTNG-SNAPSHOT(1)
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NAME

6       lttng-snapshot - Take a snapshot of an LTTng recording session
7

SYNOPSIS

9       Take a recording session snapshot:
10
11       lttng [GENERAL OPTIONS] snapshot record [--max-size=SIZE]
12             [--name=NAME] [--session=SESSION]
13             [--ctrl-url=URL --data-url=URL | URL]
14
15       Add a snapshot output to a recording session:
16
17       lttng [GENERAL OPTIONS] snapshot add-output [--max-size=SIZE]
18             [--name=NAME] [--session=SESSION]
19             (--ctrl-url=URL --data-url=URL | URL)
20
21       Show the snapshot output of a recording session:
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23       lttng [GENERAL OPTIONS] snapshot list-output [--session=SESSION]
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25       Remove the snapshot output from a recording session:
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27       lttng [GENERAL OPTIONS] snapshot del-output [--session=SESSION] 1
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DESCRIPTION

30       The lttng snapshot command can take a snapshot of, add or remove a
31       snapshot output, and show the snapshot output of:
32
33       With the --session=SESSION option
34           The recording session named SESSION.
35
36       Without the --session option
37           The current recording session (see lttng-concepts(7) to learn more
38           about the current recording session).
39
40       See lttng-concepts(7) to learn more about recording sessions.
41
42       A snapshot is a dump of the current sub-buffers of all the channels of
43       the selected recording session.
44
45       When LTTng takes a snapshot, it sends the sub-buffer dump of the
46       selected recording session to the local file system or over the network
47       to a listening relay daemon (lttng-relayd(8)). See the “Snapshot
48       output” section below to learn more.
49
50       When LTTng takes a snapshot, it does NOT clear the sub-buffers of the
51       selected recording session. In other words, different snapshots of the
52       selected recording session can contain the same event records.
53
54       You must have created the selected recording session in snapshot mode
55       (see the --snapshot option of the lttng-create(1) command as well as
56       lttng-concepts(7) to learn more about recording session modes) to use
57       the snapshot command.
58
59       A snapshot-session trigger action can also take a recording session
60       snapshot (see lttng-add-trigger(1)).
61
62       See the “EXAMPLES” section below for usage examples.
63
64       If you want, instead, to keep all the trace data, but divide it into
65       archived chunks which are then, like snapshots, ready to be processed,
66       see the recording session rotation feature in lttng-concepts(7). Trace
67       chunk archives do NOT overlap like snapshots can.
68
69       Note
70           Before you take a snapshot on a system with a high event
71           throughput, the LTTng project recommends that you first run the
72           lttng-stop(1) command. Otherwise, the snapshot could contain
73           “holes”, the result of the tracers overwriting unconsumed trace
74           packets during the snapshot operation.
75
76           After LTTng writes the snapshot trace data, you can restart the
77           recording session with the lttng-start(1) command.
78
79   Snapshot output
80       When you take a recording session snapshot with the record action,
81       LTTng writes the snapshot trace files to:
82
83       If you specify the URL non-option argument or the --ctrl-url and
84       --data-url options
85           The output defined by the URL non-option argument or by the
86           arguments of the options.
87
88           See lttng-create(1) for the format of URL.
89
90       Otherwise
91           The snapshot output of the selected recording session.
92
93           Add a snapshot output to a recording session with the add-output
94           action. As of LTTng 2.13.10, you may only add one snapshot output
95           to a given recording session.
96
97           When you create a snapshot mode recording session with the
98           --snapshot option of the lttng-create(1) command, and without its
99           --no-output option, the create command automatically adds a
100           snapshot output named snapshot-1 to the created recording session:
101
102           With its --output, --set-url, --ctrl-url, or --data-url options
103               Equivalent to using the add-output action with the provided or
104               equivalent URL(s) immediately after creating the recording
105               session.
106
107           Otherwise
108               A subdirectory, under the $LTTNG_HOME/lttng-traces ($LTTNG_HOME
109               defaults to $HOME) directory, of which the name contains the
110               recording session name and the date/time.
111
112           Show the current snapshot output of a recording session with the
113           list-output action.
114
115           Remove the snapshot output of a recording session with the del-
116           output action.
117
118       For both the record and add-output actions:
119
120       •   Assign a name to a snapshot output with the --name=NAME option.
121
122           NAME becomes part of the snapshot trace file names which LTTng
123           sends to this output.
124
125       •   By default, the snapshot files can be as big as the sum of the
126           sizes of all the sub-buffers of all the channels of the selected
127           recording session.
128
129           Set the maximum total size of all the snapshot trace files LTTng
130           writes with the --max-size option.
131

OPTIONS

133       See lttng(1) for GENERAL OPTIONS.
134
135   Recording target
136       -s SESSION, --session=SESSION
137           Take a snapshot of the sub-buffers of the recording session named
138           SESSION instead of the current recording session.
139
140   Output
141       See the “Snapshot output” section above.
142
143       -C URL, --ctrl-url=URL
144           Set the control path URL to URL.
145
146           You must also use the --data-url option.
147
148           See lttng-create(1) for the format of URL.
149
150       -D URL, --data-url=URL
151           Set the trace data path URL to URL.
152
153           You must also use the --ctrl-url option.
154
155           See lttng-create(1) for the format of URL.
156
157       -m SIZE, --max-size=SIZE
158           Set the maximum total size of all the snapshot trace files LTTng
159           writes when taking a snapshot to SIZE bytes.
160
161           The k (KiB), M (MiB), and G (GiB) suffixes are supported.
162
163       -n NAME, --name=NAME
164           Assign the name NAME to the snapshot output.
165
166   Program information
167       -h, --help
168           Show help.
169
170           This option attempts to launch /usr/bin/man to view this manual
171           page. Override the manual pager path with the LTTNG_MAN_BIN_PATH
172           environment variable.
173
174       --list-options
175           List available command options and quit.
176

EXIT STATUS

178       0
179           Success
180
181       1
182           Command error
183
184       2
185           Undefined command
186
187       3
188           Fatal error
189
190       4
191           Command warning (something went wrong during the command)
192

ENVIRONMENT

194       LTTNG_ABORT_ON_ERROR
195           Set to 1 to abort the process after the first error is encountered.
196
197       LTTNG_HOME
198           Path to the LTTng home directory.
199
200           Defaults to $HOME.
201
202           Useful when the Unix user running the commands has a non-writable
203           home directory.
204
205       LTTNG_MAN_BIN_PATH
206           Absolute path to the manual pager to use to read the LTTng
207           command-line help (with lttng-help(1) or with the --help option)
208           instead of /usr/bin/man.
209
210       LTTNG_SESSION_CONFIG_XSD_PATH
211           Path to the directory containing the session.xsd recording session
212           configuration XML schema.
213
214       LTTNG_SESSIOND_PATH
215           Absolute path to the LTTng session daemon binary (see lttng-
216           sessiond(8)) to spawn from the lttng-create(1) command.
217
218           The --sessiond-path general option overrides this environment
219           variable.
220

FILES

222       $LTTNG_HOME/.lttngrc
223           Unix user’s LTTng runtime configuration.
224
225           This is where LTTng stores the name of the Unix user’s current
226           recording session between executions of lttng(1).  lttng-create(1)
227           and lttng-set-session(1) set the current recording session.
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229       $LTTNG_HOME/lttng-traces
230           Default output directory of LTTng traces in local and snapshot
231           modes.
232
233           Override this path with the --output option of the lttng-create(1)
234           command.
235
236       $LTTNG_HOME/.lttng
237           Unix user’s LTTng runtime and configuration directory.
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239       $LTTNG_HOME/.lttng/sessions
240           Default directory containing the Unix user’s saved recording
241           session configurations (see lttng-save(1) and lttng-load(1)).
242
243       /usr/local/etc/lttng/sessions
244           Directory containing the system-wide saved recording session
245           configurations (see lttng-save(1) and lttng-load(1)).
246
247       Note
248           $LTTNG_HOME defaults to the value of the HOME environment variable.
249

EXAMPLES

251       Example 1. Take a snapshot of the current recording session, sending
252       the trace files to its snapshot output.
253
254               $ lttng snapshot record
255
256       Example 2. Take a snapshot of a specific recording session, giving it a
257       custom name.
258
259           See the --session and --name options.
260
261               $ lttng snapshot record --session=my-session --name=SNAP
262
263       Example 3. Take a snapshot of the current recording session, sending
264       the trace files to a custom location.
265
266           See the “Output directory” section of lttng-relayd(8) to understand
267           where the relay daemon to connect to (3.96.87.215) writes the
268           received traces.
269
270               $ lttng snapshot record net://3.96.87.215
271
272       Example 4. Replace the snapshot output of a specific recording session
273       with a local file system path.
274
275           See the --session option.
276
277               $ lttng snapshot del-output --session=monk 1
278               $ lttng snapshot add-output --session=monk \
279                                file:///path/to/snapshots
280
281       Example 5. Take a snapshot of the current recording session, making
282       sure its size is not over 4 MiB.
283
284           See the --max-size option.
285
286               $ lttng snapshot record --max-size=4M
287

RESOURCES

289       •   LTTng project website <https://lttng.org>
290
291       •   LTTng documentation <https://lttng.org/docs>
292
293       •   LTTng bug tracker <https://bugs.lttng.org>
294
295       •   Git repositories <https://git.lttng.org>
296
297       •   GitHub organization <https://github.com/lttng>
298
299       •   Continuous integration <https://ci.lttng.org/>
300
301       •   Mailing list <https://lists.lttng.org/> for support and
302           development: lttng-dev@lists.lttng.org
303
304       •   IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net
305

COPYRIGHT

307       This program is part of the LTTng-tools project.
308
309       LTTng-tools is distributed under the GNU General Public License
310       version 2 <http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html>.
311       See the LICENSE <https://github.com/lttng/lttng-
312       tools/blob/master/LICENSE> file for details.
313

THANKS

315       Special thanks to Michel Dagenais and the DORSAL laboratory
316       <http://www.dorsal.polymtl.ca/> at École Polytechnique de Montréal for
317       the LTTng journey.
318
319       Also thanks to the Ericsson teams working on tracing which helped us
320       greatly with detailed bug reports and unusual test cases.
321